Production of bismuth oxychloride crystals of enhanced luster and covering power

ABSTRACT

BISMUTH OXYCHLORIDE CRYSTALS OF ENHANCED LUSTER AND COVERING POWER ARE PROVIDED BY FORCING THE CRYSTAL TO GROW SMALL AND THIN. THIS ACCOMPLISHED BY HYDROLYZING BISMUTH SALT DISSOLVED IN WATER USING HYDROCHLORIC ACID WITH THE BISMUTH SALT BEING FIRST CAUSED TO FORM CRYSTAL NUCLEI USING A RELATIVELY STABLE AQUEOUS SOLUTION THEREOF IN WHICH THE BI/HCL WEIGHT RATIO IS FROM 0.2:1 TO 0.8:1, AND THEN COMPLETING CRYSTAL GROWTH USING A RELATIVELY UNSTABLE SOLUTION HAING A BI/HCL WEIGHT RATIO OF FROM 1:1 TO 2:1.

United States Patent 3 798 313 PRODUCTION OF BISNIUTH OXYCHLORIDE CRYS-TALS 0F ENHANCED LUSTER AND COVERING POWER Paul W. Wetzold, Armonk, N.Y.Paispearl Products, inc 24 Acqueduct Lane, Hastings-on-Hudson, N.Y.

0706) No Drawing. Filed Nov. 11, 1971, Ser. No. 197,975 Int. Cl. C01b11/00 US. Cl. 423-472 13 Claims ABSTRACT OF THE DISCLOSURE Bismuthoxychloride crystals of enhanced luster and covering power are providedby forcing the crystal to grow small and thin. This is accomplished byhydrolyzing bismuth salt dissolved in water using hydrochloric acid withthe bismuth salt being first caused to form crystal nuclei using arelatively stable aqueous solution thereof in which the Bi/HCl weightratio is from 0.2:1 to 0.8:1, and then completing crystal growth using arelatively unstable solution having a Bi/HCl weight ratio of from 1:1 to2: l.

The present invention relates to bismuth oxychloride crystals ofenhanced luster and covering power and the production of such crystals.

The production of bismuth oxychloride crystals for use in cosmetics toprovide an iridescent appearance is known. However, the prior artcrystals have included many large agglomerates and the ratio of averagemaximum diameter to thickness has not been greater than about 5:1. As aresult, the luster and coverage provided by these crystals has beeninadequate. The excessive thickness of the crystals is easily seen undera microscope at 600 magnifications using visible light directeddownwardly upon the crystals and then reflected back by the crystals,producing interference patterns which are directly related to thethickness. Thus, and directing attention to the smaller and flattercrystals, these are seen to possess at least about four concentricinterference rings, and are hence known as targettype crystals. Thethicker the crystals, the fatter they are in the middle, and the morerings are visible. The larger gggliomerates reveal a complex pattern ofinterference an s.

In this invention, very few large agglomerates are present, and thecrystals are characterized by being of reduced thickness in comparisonwith their average diameter. This reduced thickness is revealedparticularly by the clarity of the crystals, by the fact that some ofthem show no interference rings whatever, and by the fact that othersinclude very few interference rings, e.g., two or less. The thinnercrystals produced by this invention possess a ratio of average maximumdiameter to thickness of 8:1 or greater, frequently about 10:1.

These novel bismuth oxychloride crystals are provided, per thisinvention, by a process in which the bismuth oxychloride is produced bythe hydrolyzation of bismuth salt dissolved in water using the action ofhydrochloric acid as the hydrolyzing agent. In the process of thisinvention, a relatively stable aqueous solution of dissolved bismuthsalt is slowly introduced into a volume of water containing hydrochloricacid which is maintained at an elevated temperature in the range of fromabout 60 C. to the boiling point of water at the pressure of thereaction. This relatively stable aqueous solution has a Bi/HCl weightratio of from 0.221 to 0.8:1 and the volume of water containshydrochloric acid in an amount less than about /2% by weight to preventspontaneous hydrolyzation so that the added bismuth salt precipitatesslowly to form nuclei for further controlled crystal growth. The

growth of the crystals is completed by adding to the suspension ofcrystals produced by the slow addition of the relatively stablesolution, a relatively unstable aqueous solution of disolved bismuthsalt having a Bi/HCl weight ratio of from 1:1 to 2:1 which causescrystal growth to concentrate on the previously produced nuclei withgrowth being thereby forced to take place predominantly in the plane ofthe crystal to minimize the thickness of the crystals which are formed.

In the preferred process, the dissolved salt is bismuth nitrate and thehydrochloric acid content of the volume of water is at least .0l% byweight. The relatively stable aqueous solution is formulated to containa hydrochloric acid concentration in the range of 813% and this solutionis added, in a plurality of stages, to the volume of Water maintained ata temperature in the range of 75-99 C. to permit operation atatmospheric pressure. In the first stage, the solution is added veryslowly until a turbidity forms, indicating the generation of crystalnuclei. Thereafter, the solution can be added more rapidly. Therelatively unstable solution is desirably formulated to includehydrochloric acid in a concentration in the range of I3 18% and it ispreferably added at a rate which is at least as fast as the most rapidrate of addition of the relatively stable solution. Other preferredoperating conditions will become more fully apparent from thedescription which follows.

Referring first to the bismuth salt which is hydrolyzed, the preferredsalt is bismuth nitrate as noted hereinbefore. However, any bismuth saltwhich is soluble in water with the aid of a mineral acid may beutilized, other salts being illustrated by bismuth trichloride, bismuthoxide (which forms a salt in the mineral acid solution), bismuthcarbonate, bismuth oxycarbonate, bismuth oxynitrate, and the like.

The reaction is carried out in a volume of water maintained at elevatedtemperature, it being convenient to term this volume of water a heel.The temperature of the water in which the reaction is carried out shouldbe at least about 60 C. and is preferably higher in order that thehydrolyzation reaction may proceed smoothly and uniformly. Preferredtemperatures are from 75-99 C., and most preferably from 90-95 C. As isobvious, the reaction is preferably conducted at atmospherictemperature, but the use of pressure is possible in which event theboiling point of the water at the pressure used is not exceeded.

The volume of water must contain a small amount of hydrochloric acid(less than about /2% by weight) in order that the intial addition ofbismuth salt solution not induce uncontrolled precipitation. At leastabout .0l% is sufficient for this purpose, but normally about .02.l% isutilized.

The first objective is to produce in the heated volume of water asuspension of crystal nuclei to enable further controlled crystalgrowth. This is achieved in this invention by adding to the volume ofwater a relatively stable aqueous solution having a Bi/HCl weight ratioof from 0.221 to 0.811, preferably from 0.4:1 to 0.7:1. This relativelystable solution is introduced at a slow rate beneath the surface of thevolume of water and vigorous agitation is utilized to insure immediatedistribution of the added solution in the reaction liquor. Desirably,the relatively stable aqueous solution is added in a plurality ofstages, the subsequent stage or stages being added more rapidly than theearliest stage. Stated differentaly, the rate of addition of therelatively stable solution can be increased as soon as the reactionliquor becomes turbid indicating the presence of the desired crystalnuclei therein. As will be apparent, the initially formed nuclei growwith the addition of further solution, thus minimizing furthernucleation and leading to the production of ultimate crystals ofrelatively uniform size distribution.

After the crystal nuclei have been formed and grown to appropriate size,it is desired to complete the crystal growth emphasizing growth in theplane of the crystal while minimizing increase in the thickness of thecrystal. This is accomplished by adding to the suspension of crystalsproduced by the addition of the relatively stable solution, a relativelyunstable aqueous solution of dissolved bismuth salt.

The relatively unstable solution is formulated to contain a Bi/HClweight ratio of from 1:1 to 2: 1, preferably from 1.5:1 to 1.91:1. Ifcrystal growth is completed using a higher proportion of hydrochloricacid, then the crystals tend to agglomerate permanently to form largecrystals which are undesirable and, moreover, the yield of productdecreases undesirably. What appears to occur in the pres ence ofexcessive hydrochloric acid is the production of crystals which arecohesive with one an other causing agglomeration of the crystals in amanner which resists subsequent breakup or delamination.

In preferred practice, the relatively stable solution is formulated toinclude a hydrochloric acid concentration of 813% and the relativelyunstable solution is formulated to contain a hydrochloric acid contentof 13-18%. Also, and in order that the rate of hydrolyzation becontrolled throughout the reaction, the temperature of the reactionmedium is maintained constant from beginning to end. It is alsodesirable that the relatively unstable solution be added at a rate whichis at least as fast as the most rapid rate of addition of the relativelystable solution.

The invention is illustrated in the example which follows.

EXAMPLE There is introduced into a Pfaudler glass lined reactor of 57liter capacity equipped with an agitator, a steam jacket, and a feedline 54 liters of deionized water containing .035% of HCl (61.5 ml. of32% HCl added to the water). This solution is then heated to 90 C.

There is then provided a relatively stable aqueous solution of bismuthnitrate containing 95 grams of and 205 ml. of 32% HCl diluted to 680 ml.with deionized water. This relatively stable aqueous solution is slowlymetered into the volume of heated acidified Water in the reactor belowthe surface thereof and while the water is agitated. The starting rateof addition is 15 ml./ minute for 4 minutes after which a turbidity isobserved. Then, the addition is continued at a rate of 30 ml./minute for8 minutes and then at a rate of 63.3 ml./ minute until the solution iscompletely added.

A relatively unstable solution is made up to contain 1020 grams of Bi(NO-H O and 650 ml. of 32% HCl, diluted to 1608 ml. with deionized water.This relatively unstable solution is then added at the rate of 63.3 ml./minute until all of it has been added.

The Bi/HCl ratio of the relatively stable solution is 0.54:1 and thesame ratio of the unstable solution is 1.82:1. The HCl concentration ofthe relatively stable solution is 11:2% and the HCl concentration of theunstable solution is 15%.

The entire procedure is carried out at 90 C. and the reaction is endedas soon as all of the unstable solution has been added. The crystalssettle immediately and the clear liquor is decanted and discarded. Thecrystals are transferred to a Biichener funnel and washed with deionizedwater to neutrality. The product is then dispersed in castor oil inconventional fashion. Under the microscope it can be seenthat thelargest crystals in the field range in size from 14.4-21 microns(average 17.3) and the 20 smallest particles range from 4.77-11.6microns (average 8.2). Of the largest particles, about 30% exhibited nointerference rings and another 30% exhibited two rings or less. Theyield is 97% of theoretical.

The invention is defined in the claims which follow.

I claim:

1. A process for producing small thin crystals of bismuth oxychloride bythe hydrolyzation of bismuth salt dissolved in water by the action ofhydrochloric acid thereon, comprising slowly introducing a relativelystable aqueous solution of dissolved bismuth salt into a volume of watercontaining hydrochloric acid maintained at an elevated temperature inthe range of from about 60 C. to the boiling point of water at thepressure of reaction, said relatively stable aqueous solution having aBi/HCl weight ratio of from 0.2:1 to 0.821 and said volume of watercontaining hydrochloric acid in an amount less than about /2% by weightto prevent spontaneous hydrolyzation whereby the added bismuth saltprecipitates slowly to form nuclei for further controlled crystalgrowth, and completing the growth of said crystals by adding to thesuspension of crystals produced by the slow addition of said relativelystable solution, a relatively unstable aqueous solution of dissolvedbismuth salt, said relatively unstable solution having a Bi/HCl weightratio of from 1:1 to 2:1 to cause crystal growth to concentrate on thepreviously produced nuclei with growth being predominantly in the planeof the crystal whereby the thickness of the crystal is minimized.

2. A process as recited in claim 1 in which the dissolved salt isbismuth nitrate.

3. A process as recited in claim 2 in which the hydrochloric acidcontent of said volume of Water is at least .01% by weight.

4. A process as recited in claim 1 in which said relatively stableaqueous solution is added in stages, with the subsequent stage beingadded at a faster rate than the earliest stage.

5. A process as recited in claim 1 in which said aqueous solutions areintroduced to said volume of water beneath the surface thereof withvigorous agitation.

6. A process as recited in claim 1 in which the rate of addition of saidrelatively unstable aqueous solution is at least as fast as the mostrapid rate of addition of said relatively stable solution.

7. A process as recited in claim 1 in which the temperature ismaintained at a uniform level throughout the reaction.

8. A process as recited in claim 2 in which the concentration ofhydrochloric acid in said relatively stable solution is in the range of8-13%.

9. A process as recited in claim 2 in which the concentration ofhydrochloric acid in said relatively unstable solution is in the rangeof 13-18%.

10. A process as recited in claim 2 in which the temperature ismaintained in the range of 7599 C.

11. A process as recited in claim 2 in which the temperature ismaintained in the range of -95" C.

12. A process as recited in claim 2 in which said relatively stableaqueous solution has a Bi/HCl weight ratio of from 0.4:1 to 0.7:1.

13. A process as recited in claim 12 in which said relatively unstableaqueous solution has a Bi/HCl weight ratio of from 1.5:1 to 1.9:1.

References Cited UNITED STATES PATENTS 3/1961 Suchow 423-472 X 12/ 1923Darling 423-472 X U.S. Cl. X.R. 423617

